This invention relates to a device for preventing signal lamps from presenting a false lighting phenomenon caused by sun light, particularly from the rising sun and setting sun so that the on and off state of the signals lamps can be determined more distinctly.
In the automobile based society, the role of traffic lights is extremely important in order to control traffic smoothly. The state of traffic lights must be reliably recognizable by a driver under any circumstances.
As is well known, traffic lights are of a self-emissive type using electric bulbs. Therefore, if an ambient brightness is low, relative luminance of traffic lights is high, making the lighting state reliably recognizable, but if the surroundings are considerably bright, the relative luminance is low, making it difficult for an observer to recognize the state reliably in situations such as when the sun shines directly on surface of the traffic lights. In other words, if the sun is in a lower position as it rises or sets, the sun light is incident upon the interior of the signal lamps and reflected, thus presenting a condition that the states of the traffic lights are misidentified as being on. This is the so-called false lighting phenomenon, presents a problem that must be solved with respect to the signal lamps.
As a means for solving a false lighting phenomenon of the kind, there is known a shielding lens used for the signal lamps such as disclosed in Japanese Unexamined Utility Model Publication No. Hei-3-54100. This prior art has many cylindrical condenser lens elements having a given curvature arranged on a reverse side of lenses formed in a translucent material, and at the same time, there are formed on a front surface side of the translucent lenses diffuse lenses having converging sections forming a light transmission section corresponding to condenser lens elements. The shielding lenses have shielding films coated between the diffuse lenses and the front lenses of the signal lamps and the light sources. In other words, while the light from the electric bulb serving as the light source is condensed by the condenser lens elements for irradiation, the sun light is diffused in the interior of the signal lamps by the diffuse lenses and is also shielded by use of the shielding films in order to prevent the false lighting from taking place.
Nevertheless, in the shielding lens, when the sun light is radiant right in front of the signal lamps while the signal lamps are turned off, sun light incident upon the interior of the diffuse lens elements continuously arranged on a concave surface is allowed by the shielding element to enter the interior or the signal lamps in a straight line. Then, after the sun light is reflected by the reflection mirror in the signal lamp, it is again radiated through the condenser lens elements. As a result, a false lighting phenomenon takes place, and at the same time, the surface reflection occurs on the surface of the diffuse lens elements. Thus, due to the synergistic effect of the false lightning phenomenon, it becomes difficult to identify the on and off state of the lights. Consequently, when the sun light is incident upon the shielding lenses at a certain angle, the disclosed example demonstrates an excellent effect in preventing a false lighting phenomenon, but there is still a problem that it is difficult to prevent a false lighting phenomenon from taking place when the sun light is incident upon the front of the signal lamps at the time of the sun rise, sun set, and the like.
In short, for the prevention of a false lighting phenomenon, various improvements have been attempted, but under the present circumstances, heretofore there are no signal lamps capable of effectively solving the problem of a false lighting phenomenon because of the conflicting functions required: whereas the sun light, an external light, should be cut off as much as possible, the inner light from the internal light source should be emitted as effectively as possible.
Therefore, it is an objective of this invention to provide a device capable of emitting the inner light as effectively as possible while shielding the sun light as much as possible for preventing signal lamps from presenting a false lighting phenomenon.